The present invention relates to a method for friction stir welding using liquid cooling.
In the friction stir welding process (FSW process), the cooling of the materials to be joined is accomplished in a known manner in that the welding process is carried out completely under water. This method in particular has the disadvantage that Al/Mg alloys cannot be welded with good quality because of the high oxygen affinity and the oxygen contained in the cooling water. Moreover, in this cooling technology, the cooling water removes too much heat from the process so that it cannot be guaranteed that the materials to be joined are sufficiently plasticized. Therefore, it is possible for defects, such as pores, to occur in the weld seam because of insufficient material transport, preventing the production of a technically perfect weld seam.
However, the possibility of cooled friction stir welding of Al/Mg alloys would be of great economic importance, in particular with regard to the joining of large-surface metal sheets as occurs in aircraft construction.
Another disadvantage of the known method is that in an uncooled process, considerable distortion arises, which may result in an aftertreatment of the welded objects.
An object of the present invention is to provide a method for friction stir welding which allows welding of alloys having a high oxygen affinity and/or generation of a large amount of plasticization energy and permits easy control of the heat flux from the welding location.
The present invention provides a method for friction stir welding using liquid cooling. The method includes the steps of moving a pin tool across a welding location, spraying a cooling liquid in a localized manner from a cooling ring moving with the pin tool onto a trailing region and onto lateral regions of the welding location adjacent to the pin tool, and blowing cooling gas from a gas jet moving with the pin tool from a front of the pin tool against the pin tool and against the cooling liquid emerging from the cooling ring. In addition, the present invention provides a friction stir welding and cooling device that includes a pin tool configured to move across a welding location and a cooling ring at least partially encircling the pin tool. The cooling ring is configured to move simultaneously with the pin tool across the welding location and includes a plurality of nozzles configured to spray a cooling liquid. The nozzles are arranged such that the cooling liquid emerging from the nozzles is localized at a trailing region and at lateral regions of the welding location adjacent the pin tool.
The method according to the present invention advantageously uses a combined gas and water cooling in which the water supply to the pin tool is limited to the trailing region and the lateral regions of the pin tool, and the possible formation of a water film at the front side of the pin tool, at which the open welding location is situated, is prevented by the gas flow acting from the front.
In this context, the method according to the present invention is not limited to a specific position of the weld seam and can also be used for making horizontal weld seams.
Moreover, by adjusting the gas and water flows relative to each other, the combined gas and water cooling allows easy control of the heat flux from the welding location, thus allowing the strength in the weld seam to be adjusted in a controlled manner and the reduction in strength (xe2x80x9clocal strength dropxe2x80x9d), which usually arises in the heat-affected zone (HAZ), to be reduced in that heat is permitted where it is required for the process and dissipated where it is detrimental to the process.
A further advantage of the cooling according to the present invention can be seen in the possibility of combining the friction stir welding with a preceding laser beam, arc or flame heating, which is not possible when cooling in a water bath.
Moreover, it is possible to carry out a combined welding process for materials that are difficult to deform, the combined welding process consisting of the cooled friction stir welding process according to the present invention and a preceding laser beam welding process.